1. Field of the Invention
This invention relates to a circuit breaker and more particularly relates to an improved trip device for operating a circuit breaker mechanism to automatically open the contacts of a circuit breaker.
2. Description of the Prior Art
A trip device for tripping a circuit breaker is generally an electromagnetic device which is used to mechanically trip a circuit breaker mechanism to open the electrical contacts when the device is pulsed by a momentary low energy electrical signal supplied under abnormal or overload conditions.
In general, a trip device must be designed to reliably trip the circuit breaker mechanism under the worst set of conditions where there is a minimum capacitance and capacitor voltage, and not to be accidentally activated or triggered due to shock or vibration in the circuit breaker.
A trip device of the prior art is a magnetic trip device which is comprised of a movable keeper connected to an actuator, which when the movable keeper is released, moves as a unit to engage a trip extension that is carried on the breaker trip shaft to move the trip shaft and thereby effect opening of the breaker contacts. The magnetic trip device comprises a generally U-shaped unitary magnetic member and a movable keeper opposite the ends of the legs of the generally U-shaped unitary magnetic member with the bight portion of the generally U-shaped unitary magnetic member serving as a fixed keeper. This type of magnetic trip device is disclosed in U.S. Pat. No. 3,544,931 assigned to Westinghouse Electric Corporation and issued to N. J. Patel on Dec. 1, 1970.
One of the drawbacks of this trip device of U.S. Pat. No. 3,544,931 is that the manufacturing process requires drilling, grinding, plating and potting operations. These operations require extensive labor which translates into a substantial cost for manufacturing this trip device of the prior art. Also, the activation energy for the device, which is the energy needed to activate the device, may vary greatly. The device may generally be prone to unwanted tripping or may not trip when necessary. Also, this trip device employs a permanent magnet which tends to be costly, may be tripped by a voltage ranging from 15 to 25 volts, and may be tripped by extreme shocks and/or vibrations in a circuit breaker.
There remains, therefore, a need for a trip device for opening the electrical contacts of a circuit breaker which eliminates at least some or all of the above labor extensive operations presently required in manufacturing the trip device of the prior art, thereby reducing costs.
There also remains a need for a trip device which is activated when necessary and which still reliably holds and is not accidentally activated under extreme shock and/or vibration conditions normally occurring in a circuit breaker.